1. Field of Invention
The present invention relates to an electro-optic device that may be used in an electro-optic device, such as an active matrix drive liquid crystal device, for example. The invention also relates to an electronic instrument provided with the electro-optic device.
2. Description of Related Art
In the related art, an electro-optic device includes a pair of substrates with an electro-optic material, such as liquid crystal, interposed therebetween, and electrodes that are disposed on each of the two of substrates to apply an electric field to the electro-optic material. The electrodes are used to apply an electric field to the electro-optic material and thereby to appropriately alter a state of the electro-optic material. According to this electro-optic device, when light enters the electro-optic device from, for instance, a light source and a state of the electro-optic material is appropriately altered as mentioned above, the transmittance of the light can be controlled, and thereby image display can be realized.
One type of such an electro-optic device is provided such that, when one of the two substrates is provided with pixel electrodes arranged in matrix as the electrode, thin film transistors (hereinafter xe2x80x9cTFTxe2x80x9d) connected to each of the pixel electrodes, and scanning lines and data lines that are connected to each of the TFTs and arranged in parallel with a row and column direction, respectively, so-called active-matrix drive can be realized. Thereby, when a voltage applied to the electro-optic material is controlled for each of the pixel electrodes, or for each of the pixels divided by the scanning lines and the data lines, light transmittance can be controlled for each of the pixels.
Furthermore, in order to display a higher quality image, the electro-optic device can be provided with various configurations other than the above. For instance, typically, a storage capacitor that is formed of a pixel potential side capacitance electrode connected to the pixel electrode and the TFT and a fixed potential side capacitance electrode disposed opposite via a dielectric film to the pixel potential side capacitance electrode can be provided. This is used to hold a voltage applied to an electro-optic material for a predetermined period of time.
However, the following problems are present in the related art electro-optic device. In the electro-optic device as mentioned above, there is a universal demand in that in order to display a brighter image, an area occupied, on the substrate, by the scanning lines and the data lines or the storage capacitors, is made to be smaller, thereby a light transmission region, that is a region where a light that contributes in an actual image display in each of the pixels exits due to transmission or reflection is enlarged, and thereby an open area ratio is enhanced. In addition, in order to attain power saving, higher definition or miniaturization of the electro-optic device is simultaneously demanded. From these points of view, there is a general demand that the various kinds of constituent elements be miniaturized.
It is particularly problematic that to increase the open area ratio, a capacitance line constituting the storage capacitor also has to be miniaturized. When a width of wiring is narrowed to make the capacitance line fine, the resistance of the capacitance line becomes higher, resulting in a larger time constant of the wiring. Thereby, cross-talk or burn-in is caused. In the related art, the pixel potential side capacitance electrode that constitutes the storage capacitor is, in some examples, formed of polysilicon, tungsten silicide (WSi) or the like. However, since these materials are not necessarily low-resistance, the above problem is profoundly problematic.
As mentioned above, when each of the constituent elements is miniaturized and narrowed, sufficient attention has to also be paid to a light incidence on the TFT. That is, because when a light is incident on a channel region of a semiconductor layer that constitutes the TFT, light leakage current is caused, and thereby flicker is generated on an image, resulting in deteriorating the image quality. In particular, when the electro-optic device is used as a light valve in a projection type display device, since a light emitted from a very powerful light source is projected on the light valve, light is even more liable to enter the TFT and to cause a problem.
In the related art, in order to inhibit such light from entering the TFT, the TFT or the like is not formed on one of the two substrates, and a light shielding layer is disposed thereon. However, according to this structure, since a distance between the light shielding layer and the TFT becomes relatively larger, an effective shielding function for an obliquely entering light cannot be expected. In order to address or overcome this, the light shielding layer may be formed to be wider. However, this causes a decrease in the open area ratio. That is, the above-mentioned general demand or problems are almost impossible to address or overcome.
Furthermore, in order to inhibit light from entering the TFT, other than the above, a structure can be provided to utilize the data line as a light shielding layer. However, according to this structure, in order to decrease a signal transmission loss by as small a degree as possible, the data line is generally made of a low resistance material, such as, for instance, aluminum, accordingly the higher light reflectance thereof becomes problematic. This is because it is considered that according to such a structure, light that directly enters a surface on an incidence side of the data line can be certainly shielded, but the light reflected from the data line becomes stray light, or the light reflected from the other surface of the data line becomes stray light, resulting in light reaching the TFT. Even in such a structure, when a width of the data line is made to be wider to enhance a light shielding function, similarly to the above light shielding layer, a decrease in the open area ratio may cause a problem, and in view of the above stray light, the stray light may be contrarily increased, resulting in a rather adverse effect in view of inhibiting the light leakage current from occurring.
The present invention addresses the above and/or other problems, and provides an electro-optic device that, while realizing lower resistance of the capacitance line, or reduction or suppression of a light leakage current in the TFT, can address a general demand, such as enhancing an open area ratio. The invention also provides an electronic instrument provided with the electro-optic device.
In order to address or overcome the above problems, an electro-optic device according to the present invention includes, on a substrate; a scanning line; a data line; a thin film transistor disposed in correspondence with an intersection of the scanning line and the date line; a pixel electrode disposed in correspondence with the thin film transistor; a pixel potential side capacitance electrode that is electrically connected to the pixel electrode and constitutes a storage capacitor; and a capacitance line including a fixed potential side capacitance electrode that is disposed opposite via a dielectric film, to the pixel potential side capacitance electrode and constitutes the storage capacitor. In the above, the capacitance line has a body line portion that extends along the scanning line and a portion that extends along the data line. A width of the portion that extends along the data line in the capacitance line is formed the same as a width of the data line or wider than such a width.
According to the electro-optic device of the present invention, when a scanning signal and an image signal are supplied through the scanning line and the data line to the thin film transistor, a pixel electrode can be active matrix driven. Since a storage capacitor that is formed by oppositely disposing the pixel potential side capacitance electrode and the fixed potential side capacitance electrode is connected to the pixel electrode, a voltage of the image signal written in the pixel electrode can be retained for a long period of time.
In particular, in the present invention, since the width of a portion that extends along the data line in the capacitance line is formed the same width that of the data line or wider than such a width, the capacitance line can be made to be even lower in resistance.
Furthermore, in the present invention, as mentioned above, since the capacitance line can be made to be lower in the resistance thereof, from a viewpoint of the entire device, the capacitance line can be made to be narrower, resulting in realizing a narrower storage capacitance. Accordingly, an enhancement in the open area ratio can be attained. When referring to xe2x80x9cnarrowing the capacitance linexe2x80x9d, the capacitance line itself can be formed to have the same width as the data line, or xe2x80x9cwider than that thereofxe2x80x9d Although this could seem contradictory, since the conception of the wider width and narrower width has to be decided according to the relative relationship between the capacitance line and the data line, in view of an entire device, a xe2x80x9cnarrowing of the capacitance linexe2x80x9d can be attained in comparison with the related art device.
When referring to the wider width and narrower width, or xe2x80x9cwiderxe2x80x9d in the present invention, a specific value of the width can be appropriately and preferably determined according to theories, experiments, experiences or simulations.
Furthermore, according to the present invention, not only the resistance can be lowered as mentioned above, but also a light can be inhibited from entering the thin film transistor, in particular a channel region thereof more effectively than in the related art case. That is because, while as mentioned above, in the related art case, light reflected from a rear surface of the data line or the like becomes stray light and results in entering the thin film transistor, according to the present invention, even such stray light is likely to be blocked from proceeding by the capacitance line having the width that is the same with that of the data line or wider than such a width.
From the above, according to the present invention, due to the lower resistance of the capacitance line, a likelihood of causing problems, such as cross-talk or burn-in that is so far problematic, can be lowered. Furthermore, since a light leakage current in the thin film transistor can be reduced or suppressed from being generated, an image of higher quality can be displayed.
In the present invention, due to the presence of a portion that extends along the data line in the capacitance line, an increase in the storage capacitance can be realized. This also largely contributes in displaying an image of higher quality.
In order to allow more effective utilization of the above-mentioned light shielding function, for a material that constitutes the capacitance line, one excellent in the light shielding properties may be applied. For instance, metal elements, alloys, metal silicides, and polysilicides containing at least one of, for instance, Al (aluminum), Cu (copper), Ti (titanium), Cr (chromium), W (tungsten), Ta (tantalum), and Mo (molybdenum), and laminates thereof can be preferably used. In addition to these, a light absorptive material, such as polysilicon, can be also used.
In one exemplary embodiment of the electro-optic device according to the present invention, a periphery of a portion that extends along the data line in the capacitance line overlaps two-dimensionally with a periphery of the pixel electrode, and at least a part of the periphery of the data line does not overlap two-dimensionally with a periphery of the pixel electrode.
According to this exemplary embodiment, firstly, since the periphery of the portion along the data line in the capacitance line overlaps two-dimensionally with the periphery of the pixel electrode, in this portion, light can be shielded from entering the thin film transistor, resulting in reducing the light leakage current.
Furthermore, since at least a part of the periphery of the data line does not overlap two-dimensionally with the periphery of the pixel electrode, a parasite capacitance between the data line and the pixel electrode can be reduced. Accordingly, an adverse effect in which a potential fluctuation of the data line affects on a potential of the pixel electrode can be reduced.
From the above, according to the present exemplary embodiment, finally, quality of the display image can be heightened.
In another exemplary embodiment of the electro-optic device according to the present invention, the capacitance line is provided with, as a portion that extends along the data line, a projected portion that projects from the body line portion along the data line, and a width of the projected portion is formed to be the same as that of the data line or wider than such a width.
According to the exemplary embodiment, by making use of a region where the capacitance line is not present, in a tip end exemplary embodiment the projected portion, for instance, a contact hole that connects data line and a semiconductor layer can be disposed. That is, a degree of freedom in designing an electro-optic device can be increased.
According to still another exemplary embodiment of the present invention, a width of the body line portion in the capacitance line is formed to be wider than that of the scanning line.
According to this exemplary embodiment, even more assuredly than the above, the capacitance line can be lowered in resistance thereof, and light can be inhibited from entering the thin film transistor. In particular, when a part of the scanning line is used as a gate electrode of the thin film transistor, the light leakage current can be even more effectively inhibited from occurring in the thin film transistor. This is because, in a configuration like this, a channel region where a light should be most effectively inhibited from entering is present below the gate electrode. When the width of the capacitance line is made to be wider than that of the scanning line, a light can be more effectively inhibited from entering the channel region.
In the mode, in particular, the periphery of the body line portion in the capacitance line may be formed so as to overlap two-dimensionally with the periphery of the pixel electrode, and at least a part of the periphery of the scanning line may be formed so as not to overlap two-dimensionally with the periphery of the pixel electrode.
According to this configuration, firstly, since the periphery of the body line portion in the capacitance line overlaps two-dimensionally with the periphery of the pixel electrode, light that enters the thin film transistor can be blocked in the portion, resulting in reducing the light leakage current.
Furthermore, since at least a part of the periphery of the scanning line does not overlap two-dimensionally with the periphery of the pixel electrode, a parasite capacitance between the scanning line and the pixel electrode can be reduced. Accordingly, the potential variation in the scanning line can be reduced in adversely affecting on the potential of the pixel electrode.
From the above, consequently, according to the present exemplary embodiment, finally, the display image quality can be enhanced.
According to another exemplary embodiment of the electro-optic device of the present invention, the capacitance line is disposed in a laminated place between a semiconductor layer that constitutes the thin film transistor and the data line.
According to this exemplary embodiment, since the capacitance line is disposed at the laminated place between the semiconductor layer that constitutes the thin film transistor and the data line, light can be inhibited from entering the semiconductor layer more effectively than the above.
In the exemplary embodiment, in particular, a plurality of the pixel electrodes may be formed in a matrix on the substrate, and the capacitance line may be formed so as to be electrically connected to a lower side light shielding film that is disposed with lattice pattern below the thin film transistor and extends in matrix along the scanning line and the data line.
According to this configuration, the operational effect involving the light shield can be even more enhanced. The reason for this is that light that enters the thin film transistor is inhibited not only by the capacitance line above the thin film transistor, but also inhibited by a lower side light shielding film disposed below the thin film transistor.
Furthermore, according to the configuration, even when damage should be partially inflicted on the capacitance line, since the electrically connected lower side light shielding film may exhibit a substitute operation, the capacitance line cannot be easily made to be higher in the resistance. Furthermore, since the lower side light shielding film extends in lattice pattern along directions of the scanning line and data line, even when any damage or the like is partially inflicted not only on the capacitance line but also on the lower side light shielding film, since many electrically conductive paths can be expected, when the capacitance line is regarded as a whole, it is even more difficult for the capacitance line to become higher in the resistance.
In still another exemplary embodiment of the electro-optic device of the present invention, the capacitance line has, two-dimensionally, a notch portion corresponding to a formation site of the contact hole that electrically connects the pixel electrode and the pixel electrode side capacitance electrode.
According to this exemplary embodiment, an electrical connection between the pixel electrode and the pixel potential side capacitance electrode, regardless of the presence of the capacitance line, can be realized without difficulty, and a requirement ensuing the connection, that is, a decrease of an area of a fixed potential side capacitance electrode that partly constitutes the capacitance line, can be kept to a minimum. Accordingly, the storage capacitance can be maintained to be relatively large.
According to still another exemplary embodiment of the electro-optic device of the present invention, the capacitance line is made of a multi-layered film.
According to this exemplary embodiment, higher functionality of the capacitance line can be realized. That is, for instance, in addition to the function as the fixed potential side capacitance electrode that the capacitance line has, the capacitance line can be provided with other functions. Specifically, in order to address the above problems, when the capacitance line is constituted of a material to obtain a low resistance capacitance line and another material to realize a light shielding function capable of inhibiting light from entering the thin film transistor, the above-mentioned objective can be attained.
As in the invention, when the capacitor line is formed of a multi-layered film, the function as the storage capacitor can be stabilized. That is, for instance, when the above structure is used to realize lower resistance, the capacitance line may be constituted of only one layer of such material. However, in such a case, a function as a capacitor that the storage capacitor should have intrinsically may not be sufficiently fulfilled. By contrast, in the present invention, as mentioned above, since the capacitance line is constituted of a film of two or more layers, even when a material that has any particular function is used in one layer, a material that can work as the storage capacitor can be compensatorily used in another layer. Accordingly, the above-mentioned problems are not caused.
In the exemplary embodiment, particularly, the capacitance line is preferably formed so as to have a film made of a conductive material as an upper layer thereof, and to have a film made of a light absorbing material as a lower layer thereof.
According to this configuration, the capacitance line is allowed to have multi-functionality as described below. Firstly, since an upper layer of the capacitance line is made of a conductive material, metals, such as aluminum, copper, titanium, chromium, tantalum, and molybdenum and others, high electrical conductivity can be attained in the upper layer. In other words, according to the configuration, the narrower capacitance line, that is, the narrower storage capacitance, without further particular restrictions, can be more assuredly realized. From this, cross-talk and burn-in that are caused by the high resistance capacitance line and have been problems in the related art configuration can be more assuredly inhibited from occurring. Furthermore, the fact that the narrower capacitance line can be realized without accompanying a particular problem can largely contribute to enhance the open area ratio.
Since the lower layer of the capacitance line is made of a light absorbing material, such as polysilicon, the so-called stray light that is caused, for instance, when a light, after entering inside of the electro-optic device, is reflected by a lower surface of the data line can be inhibited in advance from reaching the TFT. That is, a total or part of such stray light is absorbed by the lower layer of the capacitance line. Accordingly, the likelihood of the stray light reaching the TFT can be more assuredly reduced.
According to still another exemplary embodiment of the electro-optic device of the present invention, the data line is formed locally wider in a portion that overlaps with the thin film transistor, and a width of a portion that extends along the data line in the capacitance line is formed to be wider than a portion that is not formed wider in the data line and the same as that of a portion that is formed wider in the data line.
According to this exemplary embodiment, a portion that overlaps with the thin film transistor in the data line is formed to be locally wider. This width of the portion that is formed to be wider is same as that of a portion that extends along the data line in the capacitance line. That is, according to this structure, above the thin film transistor, wider formed data line and capacitance line are formed. Accordingly, a light incident from above the thin film transistor can be more assuredly inhibited from entering.
More specifically, for instance, when the capacitance line is made of a refractory metal or the like, the capacitance line can by itself exhibit light shielding performance of substantially 0.1% in transmittance (2 or more in a value of OD (Optical Density)). However, when the capacitance line is subjected to the silicidation, due to a change in the composition thereof, the light shielding performance may be in some cases deteriorated. In this case, it can occur that the light shielding performance of only more than 0.1% in transmittance can be obtained.
However, in this exemplary embodiment, the data line overlapped with the capacitance line made of the refractory metal like this is also provided. Thus, when a configuration in which the overlapping of the capacitance line and the data line performs the light shielding of the thin film transistor is adopted, the light shielding performance corresponding to a multiplication of the transmittances thereof can be obtained. For instance, when the data line is made of aluminum or the like, the light shielding performance of substantially 0.001% or less in the transmittance (4 or more in the OD value) can be exhibited.
In this exemplary embodiment, in particular, the structure of a width of a portion that extends along the data line in the capacitance line is wider means that it is wider than a width of a portion that is not formed wider in the data line.
According to still another exemplary embodiment of the electro-optic device of the present invention, the data line is formed locally wider in a portion that overlaps with the thin film transistor, and a width of a portion that extends along the data line in the capacitance line is formed wider than that of a portion that is not formed wider in the data line and narrower than that of a portion that is formed wider in the data line.
According to this exemplary embodiment, a portion that overlaps with the thin film transistor in the data line is formed to be locally wider. That is, according to this, above the thin film transistor, wider formed data line and capacitance line are formed. Accordingly, light incident from above the thin film transistor can be more certainly shielded.
In the mode, in particular, a width of a portion that extends along the data line in the capacitance line is formed to be narrower than the data line that is formed wider. That is, in the portion, the data line is formed to be narrower than the capacitance line. Thereby, an increase of the stray light by reflection at the data line can be inhibited for instances, such as, when the data line is formed with, for instance, aluminum that is high in reflectance, and stray light that is generated when an incident light is reflected by some element in the electro-optic device; a return light that returns again to the electro-optic device after a light once exited from the electro-optic device is reflected by some element outside of the electro-optic device; or a return light that a light exited from the other electro-optic device returns to the electro-optic device in a projection type display device, such as a color displayable liquid crystal projector in which a plurality of sets of the electro-optic devices is disposed. This is because a portion that is formed to be wider in the data line is formed narrower in width relative to the capacitance line.
In the exemplary embodiment provided with a data line that is formed to be wider in a portion that overlaps with the thin film transistor like this, the capacitance line is disposed at a laminate position between the thin film transistor and the data line, and the data line, in addition to the portion that overlaps with the thin film transistor, may be formed to be wider in a portion where a contact hole for use in connection to the thin film transistor is disposed.
According to this configuration, even when the capacitance line as the light shielding film cannot be disposed for the contact hole, by forming the data line wider, the lowering in the light shielding performance due to the above can be compensated.
Alternatively, the data line for each of the thin film transistors may be formed to be wider continuously from a portion that overlaps with the thin film transistor up to a portion where the contact hole is disposed.
According to this configuration, the light shielding effect to the thin film transistor can be more assuredly attained.
A portion that is formed to be wider in a portion that overlaps with the thin film transistor and a portion that is formed wider in a portion where the contact hole is disposed may be separately formed wider. When a portion that overlaps with the thin film transistor and a portion where the contact hole is disposed are disposed in proximity to each other, and, as in the exemplary embodiment, formed wider continuously, there is no need of needlessly expanding a region that is formed wider. Accordingly, it is advantageous from a viewpoint of not increasing internal reflection.
According to still another mode of the electro-optic device of the present invention, the electro-optic device further includes the other substrate that is disposed opposite via an electro-optic material to the substrate, and a light shielding film disposed on the other substrate, and the width of the data line and a portion that extends along the data line in capacitance line is formed to be narrower than that of the light shielding film.
According to this exemplary embodiment, when a light is assumed to enter from the other substrate, a structure in which in sequence from an incidence side of the light, the light shielding film, the data line and the capacitance line are laminated can be formed. Here, a width of the former one thereof is wider than those of the latter two. That is, the incident light is shielded by a further wider light shielding film, and only the light transmitted therethrough can reach the data line and the capacitance line. Furthermore, when the light transmitted through the light shielding film reaches the data line and the capacitance line, these data and capacitance lines can be expected to exhibit the light shielding function. In essence, according to this exemplary embodiment, since the light shielding properties of the thin film transistor can be further heightened, the likelihood of occurrence of the light leakage current can be further reduced.
The xe2x80x9clight shielding filmxe2x80x9d in the present exemplary embodiment can be formed in a striped pattern or a lattice pattern so as to thread through a gap between the pixel electrodes, for instance, when the pixel electrodes are arranged in matrix. Furthermore, depending on the case, the light shielding film can be formed into a laminate structure in which a light absorptive material, such as chromium or chromina, and a light reflective material, such as aluminum are laminated.
An electronic instrument according to the present invention includes the electro-optic device (including its various modes) according to the present invention.
According to the electronic instrument of the present invention, due to the inclusion of the electro-optic device according to the present invention, the higher resistance of the capacitance line is not caused, and a light entering the thin film transistor can be reduced or suppressed to be as low as possible. As a result, high quality image displayable by various kinds of electronic instruments, such as a liquid crystal projector, a liquid crystal TV, a portable telephone, an electronic diary, a word processor, a viewfinder type or direct-view type video tape recorder, a work station, a video phone, a POS terminal, and a touch panel, for example, can be realized.